1. Field of the Invention
Example embodiments relate generally to a method of method of constructing a QuickConfig message in a 1x Evolution Data Only (EV-DO) communication network and method of reducing call and handoff failure rates in the 1xEV-DO network without introducing additional call setup latencies
2. Description of the Related Art
High Data Rate (HDR) is a technology originally developed for dedicated packet data applications to meet the increasing demand for wireless Internet Protocol (IP) connectivity with high spectral efficiency. Voice transmissions require low data rates, but maintain stringent delay and jitter requirements. Packet data transmissions, on the other hand, typically require bursty high data rates, with less stringent delay and jitter requirements. The HDR principle is to separate high-speed data completely from the voice network, so that the packet data requirements can be fulfilled optimally and independently.
In May 2000, the Code Division Multiple Access (CDMA) Development Group accepted HDR as the 1x Evolution (1xEV) data only (DO) system, with minor requirements for improvements. The 1x Evolution (1xEV) data only (DO) or 1xEV-DO system allows cellular service provider carriers to use one or more IS-95 CDMA radio channels to provide broadband high-speed data services to their customers. The EV-DO network is an “always-on” system that allows users to browse the Internet without complicated dialup connections. Within a 1x-EV-DO network, a high-data rate base station, whether a stand-alone node or integrated within a voice base station, operates on a 1.25 MHZ carrier that is allocated for packet data only.
The base station further employs a single shared, time division multiplexed (TDM) forward link, where only a single mobile terminal is served at any instance. The forward link throughput rate is shared by all mobile terminals. A mobile terminal selects a serving sector (or cell) of the base station by pointing its Data Rate Control (DRC) to the sector and requesting a forward data rate according to the channel condition (i.e., based on the Carrier to Interference (C/I) ratio of the channel).
FIG. 1 illustrates a Code Division Multiple Access 2000 (CDMA2000) network 100. For the purposes of illustration, the CDMA2000 network 100 operates according to the Third Generation Partnership Project (3GPP) cdma2000 Multi-Carrier Requirements in Code Division Multiple Access (CDMA) nxEV-DO (Evolution Data-Only) networks, and provides High Rate Packet Data services. The network 100 includes one or more mobile terminals (MTs) 130 in communication with an access network (AN) or base station 120. In cdma2000 systems, the mobile terminal (also known as an access terminal) is equivalent to a mobile station, and the access network is equivalent to a base station.
The CDMA2000 network 100 supports data rates up to 2 Mbps per user and uses higher order modulation schemes and a base station 120 to support such high data rates. The base station 120 provides the RF air interface (carrier 115) between a mobile terminal 130 and the network 100 via one or more transceivers. The base station 120 provides a separate 1.25 MHZ data only (DO) carrier 115 (air interface) for HDR applications for each sector 110 (or cell) served by the base station 120. A separate base station or carrier (not shown) provides the voice carrier(s) for voice applications.
The mobile terminal 130 may be a DO mobile terminal or a dual mode mobile terminal capable of utilizing both voice services and data services. To engage in a data session, the mobile terminal 130 connects to a DO carrier 115 (air interface) to use the DO high-speed data service. The data session is controlled by a Packet Data Service Node (PDSN) 160, which routes all data packets between the HDR mobile terminal 130 and the Internet 180. The PDSN 160 has a direct connection to a Packet Control Function (PCF) (not shown), which interfaces with a Base Station Controller (base station 120C) 150 of the base station 120. The base station 120C 150 is responsible for operation, maintenance and administration of the base station 120, speech coding, rate adaptation and handling of the radio resources. It should be understood that the base station 120C 150 may be a separate node or may be co-located with one or more base stations 120.
Each base station 120 is shown serving three sectors 115 (or cells). However, it should be understood that each base station 120 may serve only a single cell (referred to as an omni cell). It should also be understood that the network 100 may include multiple base stations 120, each serving one or more sectors 115, with mobile terminals 130 being capable of handing off between sectors 110 of the same base station 120 or sectors 110 of different base stations 120. For each sector 110 (or cell), the base station 120 further employs a single shared, time division multiplexed (TDM) forward link, where only a single mobile terminal 130 is served at any instance. The forward link throughput rate is shared by all mobile terminals 130. A mobile terminal 130 selects a serving sector 110 (or cell) of the base station 120 by pointing its Data Rate Control (DRC) towards the sector 115 and requesting a forward data rate according to the channel conditions (i.e., based on the Carrier to Interference (C/I) ratio of the channel).
FIG. 2 is a block diagram of a base station serving multiple mobile terminals in accordance with example embodiments of the present invention. FIG. 2 shows the base station 120 serving multiple mobile terminals 130 (MT-A, MT-B, MT-C and MT-D), each having their DRC 135 pointed at one sector 115 (sector 1) of the base station 120. The default Forward Traffic Channel Medium Access Control (FTCMAC) Protocol of the CDMA2000 network 100 defines the procedures required for the base station 120 to transmit and the mobile terminal 130 to receive the Forward Traffic Channel (FTC). This protocol operates in one of three states: (1) Inactive State, (2) Variable Rate State, and (3) Fixed Rate State: In the Inactive State, the mobile terminal 130 is not assigned a Forward Traffic Channel. In the Variable Rate State, the base station 120 transmits the Forward Traffic Channel to the mobile terminal 130 at a variable rate, as a function of the mobile terminal's DRC 135 value. In the Fixed Rate State, the base station 120 transmits the Forward Traffic Channel to the mobile terminal 130 from one particular sector 115, at one particular rate.
Once the mobile terminal 130 has pointed its DRC 135 towards a particular sector 115 specifying a requested rate, the base station 120 transmits data packets to the mobile terminal 130 on the forward traffic channel at the requested data rate. As discussed above, transmission on the forward traffic channel is time division multiplexed. At any given time, the forward traffic channel is being either transmitted or not; and if it is being transmitted, it is addressed to a single mobile terminal 130. When transmitting on the forward traffic channel, the base station 120 uses a MACIndex associated with a particular mobile terminal 130 to identify the target mobile terminal 130 for the data packets. A MACIndex is a representation of a resource that's allocated for either traffic channels or control channels. There are a maximum of 64 MAC indices defined in the standard, out of which 59 can be used for traffic channels.
FIG. 3 is a block diagram illustrating the transmission of a QuickConfig message to a mobile terminal. As shown in FIG. 3, the base station 120C 150 transmits to each of the selected mobile terminals 130 a message 145 indicating that the selected mobile terminals 130 should stop pointing their DRC 135 towards that sector 115. The message 145 is transmitted on a control channel 118 of the forward link of the base station 120. Each control channel packet contains zero or more control packets for zero or more mobile terminals 130. The control packets include messages 145 that are broadcast to mobile terminals 130 within the sector 115 over the control channel 118.
One type of message included in a control packet is an overhead message. The overhead messages in the CDMA2000 network 100 include the QuickConfig message 145 and the SectorParameters message. The SectorParameters message is used to convey sector specific information to the HDR mobile terminals 130. The QuickConfig message 145 is used to indicate a change in the contents of the overhead messages and to provide frequently changing information.
FIG. 4 illustrates the setting of each of the fields in the message shown in FIG. 3. As shown in FIG. 4, the QuickConfig message 145 includes a number of fields 148 and a setting 149 for each of the fields 148. The Message ID field indicates that the message is a QuickConfig message. The Color Code and Sector ID fields indicate the color code and ID of the sector 115 transmitting the QuickConfig message 145. The Sector Signature field is set to the value of the Sector Signature field of the next SectorParameters message that will be transmitted.
Similarly, the Access Signature field is set to the value of the Access Signature parameter from the AccessParameters message, which is transmitted on an Access Channel (not shown) of the forward link. The Redirect field is used to indicate whether or not the network 100 is redirecting all mobile terminals 130 away from the sector 115.
The RPC Count field is set to the maximum number of Reverse Power Control (RPC) channels supported by the sector 115. For each RPC Count occurrence (i.e., for each mobile terminal), a DRC Lock field is set to “1” if the network 100 has received a valid DRC 135 from the mobile terminal 130 that has been assigned a MACIndex. Each occurrence n of the DRC Lock field is associated with MACIndex 64-n (e.g., occurrence 1 of this field corresponds to MACIndex 63). Otherwise, the DRC Lock field is set to “0”. Similarly, for each RPC Count occurrence n, a Forward Traffic (FT) Valid field is set to “1” if the forward traffic channel associated with MACIndex 64-n is valid. The Reserved field includes six bits and is usually set to zero.
Accordingly, in EV-DO systems such as the CDMA2000 network 100 shown in FIGS. 1-3, the QuickConfig message 145 is sent by the base station 120 as part of the broadcast control channel or overhead messages. In the QuickConfig message 145, the FTValid field is used for Forward Traffic Channel MAC (FTCMAC) layer supervision.
Based on how the base station 120 software is structured into application software and driver software (which can potentially run on different processors at the base station 120), the application software at base station 120 has to construct the QuickConfig message 145 at what is referred to as a control channel “buildback” time (“first timing”). This first timing is a few slots before the start of the control channel cycle for transmission by the driver software over the air interface 115 at a control channel start time (“second timing” e.g., the start time of the next control channel cycle).
A time interval between the first and second timings can be understood as a control channel build interval (T). If any call allocation for a mobile terminal 130 occurs during this interval T, then the QuickConfig message 145 has already been constructed for transmission in the subsequent control channel cycle.
The FTValid bit in the FTValid field of the QuickConfig message 145 is set based on the set of open traffic channels on the base station 120. Thus, for mobile terminals 130 whose traffic channels are first opened during the control channel build interval T, their traffic channel was not open at the first timing when the QuickConfig message was originally constructed. Hence, the FTValid bit is not set in the QuickConfig message 145 for mobile terminals 130 whose traffic channels were first opened during the control channel build interval T. This can lead to FTCMAC layer supervision errors at the mobile terminal 130, causing call or handoff failures.
For example, FTCMAC layer supervision at the mobile terminal 130 starts as soon as mobile terminal 130 receives a TrafficChannelAssignment (TCA) message. At that point, the mobile terminal 130 starts monitoring the FTValid bit in the QuickConfig message, which as noted above is received as part of broadcast control channel messages. If the bit in the FTValid field in the QuickConfig message 145 is set to false, i.e., a logic low or “0”, then the mobile terminal 130 assumes a failure in FTCMAC layer supervision and drops the call on its side. This causes a call failure in an EV-DO system such as network 100.
Thus, in the existing method of constructing the QuickConfig message 145 in the base station 120, if the allocation of traffic channel resources on the base station 120 and transmission of the TCA message to a mobile terminal 130 informing the mobile terminal 130 about allocation of traffic channel resources happens during the control channel build interval T, then the mobile terminal 130 will fail FTCMAC layer supervision. This is because the QuickConfig message 145 sent by the base station 120 will have the bit in the FTValid field set to false. In other words, the mobile terminal 130 drops the call.
A possible way to avoid this is to delay the transmission of the TCA to the mobile terminal 130 to beyond the second timing at which the next control channel cycle starts, i.e., push it to outside the control channel build interval T. However, in a worst case scenario this causes a significant delay of the control channel build interval T for call setup. For delay sensitive applications such as Push-To-Talk (PTT), this setup delay may be unacceptable and would hold up system resources for a longer duration, preventing these resources from being allocated to other calls.